Field of the Invention
Embodiments disclosed herein relate to an automated meter to measure the electrical stability of drilling fluids. More specifically, embodiments disclosed herein relate to a drilling fluid analyzer for determining viscosity, gel strength, and or electric stability. More specifically still, embodiments disclosed herein relate to methods and systems for determining viscosity, gel strength, and or electric stability of drilling fluids that include automation and remote control.
Background Art
When drilling oil and/or gas wells, oil-based drilling fluids are often used to cool the drill bit, remove rock chips, and control subsurface fluids. Various properties of this fluid can be measured to compute useful results. For example, the electrical stability of drilling fluid is a property that is typically measured using an electrical stability (ES) test. The ES test is typically a manual test that is performed by a mud engineer or an equivalent technician. Conventionally, when performing an ES test, a probe that includes circular flat electrodes of diameter ⅛ inch, spaced 1/16 inch between faces, is inserted into the drilling fluid. Drilling fluid, which contains non-aqueous fluid, water (or other polar liquid), clays, and other materials, fills the gap between the two electrodes of the test probe. Wires run from the probe to a signal generator and measurement meter, which ramps the voltage between the electrodes until components of the fluid align to form a short-circuiting bridge. When the short circuit occurs, the current between the electrodes immediately spikes. Specifically, an AC voltage of 340 Hz is ramped at 150 V s−1 until a peak current (approximately 61 μA) occurs. At this stage, the peak voltage, known as the breakdown voltage (VBD) is captured by the meter. 61 μA is the current at which the breakdown voltage occurs for the above-described geometry of the probe. The breakdown voltage is the voltage at which the drilling fluid's electrical properties become electric field-dependent and is the voltage at which the electrical conductivity of the drilling fluid becomes non-ohmic. Thus, the breakdown voltage is related to the emulsion stability and is then used to compute the emulsion stability and other properties of the drilling fluid.
Typically, to measure the electrical stability of drilling fluid using the above manual probe method, the drilling fluid and associated fluid is kept static, as movement and shifts in the fluids of the drilling fluid may cause the measurements taken by the electrodes and recorded by the meter to be skewed. In addition, when using the manual probe method described above, the electrodes and the gap between electrodes of the probe are manually cleaned after each measurement sampling.
In addition to measuring electrical stability, drilling rig operators may perform tests to determine viscosity. Typically, such measurements were performed with instruments such as a Marsh funnel viscometer. Marsh funnels are manually operated measurement devices that provide a drilling operator a general idea as to the viscosity of a particular fluid. In use, the funnel is held vertically and the end tube closed by covering the outlet with a finger. Fluid to be measured is then poured into the funnel until the fluid reaches a line indicating about 1.5 liters. To take the measurement, the finger is removed from the outlet and a stopclock is started. The fluid exits the funnel and the time to remove one quart of fluid from the funnel is recorded. With a known volume and a discharge time, the viscosity may be calculated.
While such measurement techniques give operators a general idea as to the viscosity, due to the manual implementation, the results may not always be accurate. Additionally, the viscosity of the fluid downhole is not truly known, because the fluid cannot be heated or measured under pressure.
In addition to electrical stability and viscosity, the gel strength of the fluid can also be determined. Gel strength is the measure of a fluid's ability to hold particles in suspension, and the gel strength is measure using a concentric cylinder viscometer. Gel strength is also measured manually and the results analyzed when adjusting the properties of the drilling fluid.
Accordingly, there exists a need for an automated method for measuring the electrical stability, viscosity, and/or gel strength of drilling fluid. Additionally, there exists a need for improved methods for sampling drilling fluid for appropriate measurements and cleaning of the electrodes of the probe used to measure the breakdown voltage of the drilling fluid.